ii)  A tachyon  has \(s_1=1\)  and \(s_2=-1\) . The classical
dynamics of tachyons is described in the literature, e.g., in
[1]}, [2]}, but, for our purposes, it is sufficient
to give only a basic survey.
For a relatively small momentum \(k=\vert {{\bf k}}\vert \) , there is
\(m_k^2 < 0\)  in Eq. (), and the equation of motion is
\({\ddot{h}} - \omega ^2 h \,=\,0\,,\qquad \omega ^2 = \left|m_k^2\right|\,,\) 
